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如何實(shí)現(xiàn)定時(shí)推送的具體方案

更新時(shí)間：2021年04月19日 17:33:40 作者：dotNet源計(jì)劃

在工作當(dāng)中遇到了一個(gè)需要定時(shí)向客戶端推送新聞、文章等內(nèi)容。小項(xiàng)目又用不了大框架,這個(gè)時(shí)候在網(wǎng)上搜了很久沒(méi)有找到合適的解決方案,直到看到了一位大佬寫(xiě)的文章提供了一個(gè)非常不錯(cuò)的思路本篇文章也是受到他的啟發(fā)實(shí)現(xiàn)了之后這里分享給大家

詳細(xì)內(nèi)容

詳細(xì)內(nèi)容大概分為4個(gè)部分，1.應(yīng)用場(chǎng)景 2.遇到問(wèn)題 3.設(shè)計(jì) 4.實(shí)現(xiàn) 5.運(yùn)行效果

1.應(yīng)用場(chǎng)景

需要定時(shí)推送數(shù)據(jù)，且輕量化的實(shí)現(xiàn)。

2.遇到問(wèn)題

如果啟動(dòng)一個(gè)定時(shí)器去定時(shí)輪詢
（1）輪詢效率比較低
（2）每次掃庫(kù)，已經(jīng)被執(zhí)行過(guò)記錄，仍然會(huì)被掃描（只是不會(huì)出現(xiàn)在結(jié)果集中），會(huì)做重復(fù)工作
（3）時(shí)效性不夠好，如果每小時(shí)輪詢一次，最差的情況下會(huì)有時(shí)間誤差
如何利用“延時(shí)消息”，對(duì)于每個(gè)任務(wù)只觸發(fā)一次，保證效率的同時(shí)保證實(shí)時(shí)性，是今天要討論的問(wèn)題。

3.設(shè)計(jì)

高效延時(shí)消息，包含兩個(gè)重要的數(shù)據(jù)結(jié)構(gòu)：

環(huán)形隊(duì)列，例如可以創(chuàng)建一個(gè)包含3600個(gè)slot的環(huán)形隊(duì)列（本質(zhì)是個(gè)數(shù)組）
任務(wù)集合，環(huán)上每一個(gè)slot是一個(gè)Set

同時(shí)，啟動(dòng)一個(gè)timer，這個(gè)timer每隔1s，在上述環(huán)形隊(duì)列中移動(dòng)一格，有一個(gè)Current Index指針來(lái)標(biāo)識(shí)正在檢測(cè)的slot。

Task結(jié)構(gòu)中有兩個(gè)很重要的屬性：

Cycle-Num：當(dāng)Current Index第幾圈掃描到這個(gè)Slot時(shí)，執(zhí)行任務(wù)
Task-Function：需要執(zhí)行的任務(wù)指針

假設(shè)當(dāng)前Current Index指向第一格，當(dāng)有延時(shí)消息到達(dá)之后，例如希望3610秒之后，觸發(fā)一個(gè)延時(shí)消息任務(wù)，只需：

計(jì)算這個(gè)Task應(yīng)該放在哪一個(gè)slot，現(xiàn)在指向1，3610秒之后，應(yīng)該是第11格，所以這個(gè)Task應(yīng)該放在第11個(gè)slot的Set中
計(jì)算這個(gè)Task的Cycle-Num，由于環(huán)形隊(duì)列是3600格（每秒移動(dòng)一格，正好1小時(shí)），這個(gè)任務(wù)是3610秒后執(zhí)行，所以應(yīng)該繞3610/3600=1圈之后再執(zhí)行，于是Cycle-Num=1

Current Index不停的移動(dòng)，每秒移動(dòng)到一個(gè)新slot，這個(gè)slot中對(duì)應(yīng)的Set，每個(gè)Task看Cycle-Num是不是0：

如果不是0，說(shuō)明還需要多移動(dòng)幾圈，將Cycle-Num減1
如果是0，說(shuō)明馬上要執(zhí)行這個(gè)Task了，取出Task-Funciton執(zhí)行（可以用單獨(dú)的線程來(lái)執(zhí)行Task），并把這個(gè)Task從Set中刪除

使用了“延時(shí)消息”方案之后，“訂單48小時(shí)后關(guān)閉評(píng)價(jià)”的需求，只需將在訂單關(guān)閉時(shí)，觸發(fā)一個(gè)48小時(shí)之后的延時(shí)消息即可：

無(wú)需再輪詢?nèi)坑唵?，效率?/li>
一個(gè)訂單，任務(wù)只執(zhí)行一次
時(shí)效性好，精確到秒（控制timer移動(dòng)頻率可以控制精度）

4.實(shí)現(xiàn)

首先寫(xiě)一個(gè)方案要理清楚自己的項(xiàng)目結(jié)構(gòu)，我做了如下分層。

Interfaces ，這層里主要約束延遲消息隊(duì)列的隊(duì)列和消息任務(wù)行。

public interface IRingQueue<T>
{
    /// <summary>
    /// Add tasks [add tasks will automatically generate: task Id, task slot location, number of task cycles]
    /// </summary>
    /// <param name="delayTime">The specified task is executed after N seconds.</param>
    /// <param name="action">Definitions of callback</param>
    void Add(long delayTime,Action<T> action);
    /// <summary>
    /// Add tasks [add tasks will automatically generate: task Id, task slot location, number of task cycles]
    /// </summary>
    /// <param name="delayTime">The specified task is executed after N seconds.</param>
    /// <param name="action">Definitions of callback.</param>
    /// <param name="data">Parameters used in the callback function.</param>
    void Add(long delayTime, Action<T> action, T data);
    /// <summary>
    /// Add tasks [add tasks will automatically generate: task Id, task slot location, number of task cycles]
    /// </summary>
    /// <param name="delayTime"></param>
    /// <param name="action">Definitions of callback</param>
    /// <param name="data">Parameters used in the callback function.</param>
    /// <param name="id">Task ID, used when deleting tasks.</param>
    void Add(long delayTime, Action<T> action, T data, long id);
    /// <summary>
    /// Remove tasks [need to know: where the task is, which specific task].
    /// </summary>
    /// <param name="index">Task slot location</param>
    /// <param name="id">Task ID, used when deleting tasks.</param>
    void Remove(long id);
    /// <summary>
    /// Launch queue.
    /// </summary>
    void Start();
}
 public interface ITask
 {
 }

Achieves，這層里實(shí)現(xiàn)之前定義的接口，這里寫(xiě)成抽象類(lèi)是為了后面方便擴(kuò)展。

using System;
using System.Collections.Concurrent;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using DelayMessageApp.Interfaces;
namespace DelayMessageApp.Achieves.Base
{
public abstract class BaseQueue<T> : IRingQueue<T>
{
    private long _pointer = 0L;
    private ConcurrentBag<BaseTask<T>>[] _arraySlot;
    private int ArrayMax;
    /// <summary>
    /// Ring queue.
    /// </summary>
    public ConcurrentBag<BaseTask<T>>[] ArraySlot
    {
        get { return _arraySlot ?? (_arraySlot = new ConcurrentBag<BaseTask<T>>[ArrayMax]); }
    }
    public BaseQueue(int arrayMax)
    {
        if (arrayMax < 60 && arrayMax % 60 == 0)
            throw new Exception("Ring queue length cannot be less than 60 and is a multiple of 60 .");
        ArrayMax = arrayMax;
    }
    public void Add(long delayTime, Action<T> action)
    {
        Add(delayTime, action, default(T));
    }
    public void Add(long delayTime,Action<T> action,T data)
    {
        Add(delayTime, action, data,0);
    }
    public void Add(long delayTime, Action<T> action, T data,long id)
    {
        NextSlot(delayTime, out long cycle, out long pointer);
        ArraySlot[pointer] =  ArraySlot[pointer] ?? (ArraySlot[pointer] = new ConcurrentBag<BaseTask<T>>());
        var baseTask = new BaseTask<T>(cycle, action, data,id);
        ArraySlot[pointer].Add(baseTask);
    }
    /// <summary>
    /// Remove tasks based on ID.
    /// </summary>
    /// <param name="id"></param>
    public void Remove(long id)
    {
        try
        {
            Parallel.ForEach(ArraySlot, (ConcurrentBag<BaseTask<T>> collection, ParallelLoopState state) =>
            {
                var resulTask = collection.FirstOrDefault(p => p.Id == id);
                if (resulTask != null)
                {
                    collection.TryTake(out resulTask);
                    state.Break();
                }
            });
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
        }
    }
    public void Start()
    {
        while (true)
        {
            RightMovePointer();
            Thread.Sleep(1000);
            Console.WriteLine(DateTime.Now.ToString());
        }
    }
    /// <summary>
    /// Calculate the information of the next slot.
    /// </summary>
    /// <param name="delayTime">Delayed execution time.</param>
    /// <param name="cycle">Number of turns.</param>
    /// <param name="index">Task location.</param>
    private void NextSlot(long delayTime, out long cycle,out long index)
    {
        try
        {
            var circle = delayTime / ArrayMax;
            var second = delayTime % ArrayMax;
            var current_pointer = GetPointer();
            var queue_index = 0L;
            if (delayTime - ArrayMax > ArrayMax)
            {
                circle = 1;
            }
            else if (second > ArrayMax)
            {
                circle += 1;
            }
            if (delayTime - circle * ArrayMax < ArrayMax)
            {
                second = delayTime - circle * ArrayMax;
            }
            if (current_pointer + delayTime >= ArrayMax)
            {
                cycle = (int)((current_pointer + delayTime) / ArrayMax);
                if (current_pointer + second - ArrayMax < 0)
                {
                    queue_index = current_pointer + second;
                }
                else if (current_pointer + second - ArrayMax > 0)
                {
                    queue_index = current_pointer + second - ArrayMax;
                }
            }
            else
            {
                cycle = 0;
                queue_index = current_pointer + second;
            }
            index = queue_index;
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
            throw;
        }
    }
    /// <summary>
    /// Get the current location of the pointer.
    /// </summary>
    /// <returns></returns>
    private long GetPointer()
    {
        return Interlocked.Read(ref _pointer);
    }
    /// <summary>
    /// Reset pointer position.
    /// </summary>
    private void ReSetPointer()
    {
        Interlocked.Exchange(ref _pointer, 0);
    }
    /// <summary>
    /// Pointer moves clockwise.
    /// </summary>
    private void RightMovePointer()
    {
        try
        {
            if (GetPointer() >= ArrayMax - 1)
            {
                ReSetPointer();
            }
            else
            {
                Interlocked.Increment(ref _pointer);
            }
            var pointer = GetPointer();
            var taskCollection = ArraySlot[pointer];
            if (taskCollection == null || taskCollection.Count == 0) return;
            Parallel.ForEach(taskCollection, (BaseTask<T> task) =>
            {
                if (task.Cycle > 0)
                {
                    task.SubCycleNumber();
                }
                if (task.Cycle <= 0)
                {
                    taskCollection.TryTake(out task);
                    task.TaskAction(task.Data);
                }
            });
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
            throw;
        }
    }
}
}
using System;
using System.Threading;
using DelayMessageApp.Interfaces;
namespace DelayMessageApp.Achieves.Base
{
public class BaseTask<T> : ITask
{
    private long _cycle;
    private long _id;
    private T _data;
    public Action<T> TaskAction { get; set; }
    public long Cycle
    {
        get { return Interlocked.Read(ref _cycle); }
        set { Interlocked.Exchange(ref _cycle, value); }
    }
    public long Id
    {
        get { return _id; }
        set { _id = value; }
    }
    public T Data
    {
        get { return _data; }
        set { _data = value; }
    }
    public BaseTask(long cycle, Action<T> action, T data,long id)
    {
        Cycle = cycle;
        TaskAction = action;
        Data = data;
        Id = id;
    }
    public BaseTask(long cycle, Action<T> action,T data)
    {
        Cycle = cycle;
        TaskAction = action;
        Data = data;
    }
    public BaseTask(long cycle, Action<T> action)
    {
        Cycle = cycle;
        TaskAction = action;
    }
    public void SubCycleNumber()
    {
        Interlocked.Decrement(ref _cycle);
    }
}
}

Logic，這層主要實(shí)現(xiàn)調(diào)用邏輯，調(diào)用者最終只需要關(guān)心把任務(wù)放進(jìn)隊(duì)列并指定什么時(shí)候執(zhí)行就行了，根本不需要關(guān)心其它的任何信息。

public static void Start()
{
    //1.Initialize queues of different granularity.
    IRingQueue<NewsModel> minuteRingQueue = new MinuteQueue<NewsModel>();
    //2.Open thread.
    var lstTasks = new List<Task>
    {
        Task.Factory.StartNew(minuteRingQueue.Start)
    };
    //3.Add tasks performed in different periods.
    minuteRingQueue.Add(5, new Action<NewsModel>((NewsModel newsObj) =>
    {
        Console.WriteLine(newsObj.News);
    }), new NewsModel() { News = "Trump's visit to China！" });
    minuteRingQueue.Add(10, new Action<NewsModel>((NewsModel newsObj) =>
    {
        Console.WriteLine(newsObj.News);
    }), new NewsModel() { News = "Putin Pu's visit to China！" });
    minuteRingQueue.Add(60, new Action<NewsModel>((NewsModel newsObj) =>
    {
        Console.WriteLine(newsObj.News);
    }), new NewsModel() { News = "Eisenhower's visit to China！" });
    minuteRingQueue.Add(120, new Action<NewsModel>((NewsModel newsObj) =>
    {
        Console.WriteLine(newsObj.News);
    }), new NewsModel() { News = "Xi Jinping's visit to the US！" });
    //3.Waiting for all tasks to complete is usually not completed. Because there is an infinite loop.
    //F5 Run the program and see the effect.
    Task.WaitAll(lstTasks.ToArray());
    Console.Read();
}

Models，這層就是用來(lái)在延遲任務(wù)中帶入的數(shù)據(jù)模型類(lèi)而已了。自己用的時(shí)候換成任意自定義類(lèi)型都可以。